Comparing i.v. BU dose intensity between two regimens (FB2 vs FB4) for allogeneic HCT for AML in CR1: a report from the Acute Leukemia Working Party of EBMT

This retrospective analysis compared two regimens of fludarabine combined with i.v. BU 6.4 mg/kg (FB2) or BU 12.8 mg/kg (FB4) for allografting of AML in first CR. A total of 437 patients (median age: 50 years) were administered FB2 (n = 225, 51%) or FB4 (n = 212, 49%). Median follow-up time was 28 months. Use of FB2 resulted in a longer time to neutrophil engraftment (17 vs 15 days, P<0.0001) but no difference in incidence of grade II-IV acute (P = 0.54) or chronic GVHD (P = 0.51). In patients <50 years of age, FB2 was associated with a higher 2-year cumulative incidence of relapse (33 +/- 6% vs 20 +/- 4%, P = 0.04), but there was no difference in 2-year leukemia-free survival (LFS) (P = 0.45), OS (P = 0.53) or non-relapse mortality (P = 0.17). In recipients >= 50 years of age, FB2 resulted in better 2-year LFS (63 +/- 4% vs 42 +/- 7%, P = 0.02) and OS (68 +/- 4% vs 45 +/- 7%, P = 0.006); a lower 2-year non-relapse mortality, albeit not statistically significant (15 +/- 3% vs 29 +/- 6%, P = 0.06), was observed with FB2. FB2 is an effective and well-tolerated regimen in patients >= 50 years of age and does not compromise survival when used in patients <50 years undergoing allogeneic transplantation for AML in first CR.